Terpolymers comprising 90% or more propylene having a DSC melting point lower than 140.degree.-145.degree. C. cannot be prepared in hexane slurry at 60.degree. C. because the polymer particles swell by absorbing the hexane diluent, become very sticky, and thereby cause agglomeration and reactor fouling. While the use of 1-butene as a termonomer along with small amounts of ethylene is not new, its advantage over ethylene of not increasing the solubility of the polymer as much as ethylene has not been fully utilized in the past because a satisfactory method of manufacturing the polymer has not been conceived to take advantage of the unique contributions of 1-butene while also benefiting from the use of ethylene to modify a basically polypropylene product.
In the past, numerous combinations of monomers, principally ethylene and propylene, have been introduced into the same or different reactors with or without the presence of a chain terminator such as hydrogen between the stages. See, for example, U.S. Pat. Nos. Davison et al 2,839,515, Edmonds, Jr. 3,970,719, Cox 3,264,184, Short 3,318,976, Kontos 3,378,606, Hassell 3,378,608, Hagemeyer, Jr. et al 3,529,037, Gobran et al 3,649,579, Koga et al 3,974,236, and Shiga et al 4,254,237. Many such processes have as their objective the manufacture of block copolymers and/or dispersions of particles in a matrix in which particles of one structure are evenly distributed within a medium comprising a polymer of another, more or less modified, polymer. Both batch and continuous processes for producing such composite products are found in the prior art.
The reader may also be interested in U.S. Pat. No. Shirai et al 3,642,951, Saito et al 4,066,718, Furutachi et al 4,128,606, and particularly Scoggin 3,525,781, which teaches preparing block copolymers continuously by feeding batch prepolymers into a continuous polymerization zone, Baba et al U.S. Pat. No. 4,433,110, which provides propylene and 1-butene polymerization in a first stage and propylene and ethylene polymerization in a second stage, and particularly Frese et al 3,959,409, which discloses the production of crystalline propylene/ethylene/butene-1 terpolymers in series-connected reactors, the ethylene being introduced only in the second or subsequent reactors. See also the large number of examples of terpolymer production in Suzuki et al U.S. Pat. No. 4,304,890. The feed of ethylene is increased, compared to propylene, after the first stage in Sennari et al U.S. Pat. No. 3,670,053.
We are not aware of any rationale in the prior art for utilizing 1-butene to facilitate the manufacture of low melting point polymers of propylene and a small amount of ethylene.